The present invention was made during the development of a hydraulic actuator for moving outboard portions of airplane wings between spread and folded positions relative to inboard portions of the wings. However, the invention has uses in other actuators as well, such as, for example, actuators used in airplane thrust reverser systems.
It is known to provide hydraulic actuators with internal locking mechanisms for mechanically locking the actuators in either a fully extended or a fully retracted position. In known actuators which include a locking mechanism, there are loads on the actuators which also load the lock mechanism. In these actuators, the load acting on the lock mechanism during unlocking results in wear and a reduced life for the lock mechanism. It is therefore desirable to unload the lock mechanism from both internal and external loads before unlocking.
A principal object of the invention is to provide a lock mechanism for a hydraulic actuator which can be unloaded before being operated to unlock the actuator.
In known actuators having lock mechanisms, the lock mechanism is released by application of hydraulic pressure into a working chamber of the actuator. Inadvertent application of pressure will both unlock and deploy the actuator. In many installations it is desirable to prevent inadvertent deployment. Accordingly, an important object of this invention is to provide a lock mechanism for a hydraulic actuator which cannot be deployed by inadvertent pressure introduction into a working chamber.
In thrust reverser systems, it is known to prevent inadvertent deployment by use of electric or hydraulic powered locks which are relatively heavy, relatively expensive and not completely reliable. Another object of the present invention is to provide a hydraulically controlled lock mechanism which is believed to be lighter, less expensive and more reliable than the known electric and hydraulic mechanisms.
Actuators in the patent literature, including some type of lock mechanism, are disclosed by the following U.S. patents: U.S. Pat. No. 3,320,861, granted May 23, 1967 to Harry J. Johnson and Marvin J. Hiemstra; U.S. Pat. No. 3,584,544, granted Jun. 15, 1971 to Robert W. Haberman; U.S. Pat. No. 3,812,766, granted May 28, 1974, to Dieter Weiss; U.S. Pat. No. 4,470,340, granted Sep. 11, 1984, to Kip B. Goans and Neil H. Akkerman; U.S. Pat. No. 4,712,471, granted Dec. 15, 1987, to D. Dale Johnson; U.S. Pat. No. 5,056,418, granted Oct. 15, 1991 to Stanley W. Granger, Joseph O. Beard and Frode Sveen; U.S. Pat. No. 5,081,910, granted Jan. 21, 1992, to Frank D'Ascenzo, Jr.; U.S. Pat. No. 5,097,748, granted Mar. 24, 1992, to Georg Koch, Wolfgang Traupe, Frank van de Poel, Kurt Schaible, and Holger Seel; and U.S. Pat. No. 5,176,227, granted Jan. 5, 1993 to William H. Kohler.